Method of adjusting idle speed of an internal combustion engine

Abstract

Idle speed of an internal combustion engine is adjusted by applying a drive signal having a predetermined value to a flow rate control mechanism which is disposed in a main bypass passage bypassing a throttle valve while the flow rate control mechanism is energized by the drive signal to operate the engine at close to a desired idling speed, a flow rate adjustment screw in a second bypass passage also bypassing the throttle valve is adjusted to cause the actual speed of the engine to become equal to the desired idle speed.

I claim: 
     
       1. A method of adjusting the idle speed of an internal combustion engine having an intake passage, a throttle valve in the intake passage, main and second bypass passages, each of which separately communicates with the intake passage so as to bypass the throttle valve, flow rate adjustment means in said second bypass passage, and flow rate control means in said main bypass passage, the opening degree of said flow rate control means being controlled in accordance with the rotational speed of the engine, said method comprising the steps of: applying a drive signal having a predetermined fixed value independent of the actual rotational speed of the engine to the flow rate control means so as to operate the engine at a speed above its lowest operating speed; and   while the flow rate control means is energized by said drive signal, adjusting the flow rate adjustment means so that the actual rotational speed of the engine becomes equal to a desired idling speed.   
     
     
       2. The method as claimed in claim 1 in which the drive signal applied to the flow rate control means has a predetermined value to operate the engine at a speed close to the desired idling speed. 
     
     
       3. The method as claimed in claim 1 comprising the additional step of warming up the engine to substantially its normal operating temperature prior to applying the drive signal to the flow rate control means to operate the engine at a speed above its lowest operating speed. 
     
     
       4. The method of claim 1 comprising the additional steps of: warming up the engine to a temperature less than the normal operating temperature prior to applying the drive signal to the flow rate control means to operate the engine at a speed above its lowest operating speed; and   modifying the value of the drive signal from said predetermined value by an amount that is a function of the temperature of the engine at the time of adjusting the idling speed thereof.   
     
     
       5. The combination comprising: an internal combustion engine;   an intake passage therefor;   a throttle valve in the intake passage;   a main bypass passage connected to the intake passage upstream and downstream of the throttle valve to bypass the throttle valve;   a second bypass passage connected to the intake passage upstream and downstream of the throttle valve to bypass the throttle valve;   flow rate adjustment means in the second bypass passage;   flow rate control means in the main bypass passage;   sensor means to sense the temperature and operating speed of the engine;   a control circuit connected to the sensor means to receive signals therefrom and connected to the flow rate control means to control the passage of air through the main bypass passage to maintain the idling speed of the engine as a function of the temperature of the engine; and   a separate drive signal generator connected to the flow rate control means to control the operation thereof during initial adjust of the idling speed of the engine, the drive signal generator providing a predetermined drive signal to set the flow rate control means to a value to operate the engine at a speed above its lowest operating speed while the flow rate adjustment means in the second bypass passage is being adjusted.